During the lead reduction program in the last 15 years the principal source of increased gasoline octane was aromatics.
Aromatics content of gasoline is currently 30% or higher and it may contain more than 40% aromatics.
Recently, the Clean Air Act required the reduction of aromatics and benzene in the gasoline pool. CRU reformate is a major stream in the gasoline pool. Refineries are faced with the prospect of supplying reformulated gasoline to meet tightened automotive emission standards. Reformulated gasoline would differ from existing products in having a lower vapor pressure, lower final boiling point, increased content of oxygenates and lower content of olefins, benzene and aromatics. The aromatics content may be lowered over several years to a maximum of as low as 20%. Rising fuel quality demands of high-performance internal-combustion engines have compelled petroleum refineries to install new and modified processes for increased "octane" or knock resistance in the gasoline pool. A number of options have been used by refineries to accomplish this. Some methods include higher-severity catalytic cracking, higher fluid catalytic cracking gasoline octane, isomerization of light naphtha and the use of oxygenated compounds.
Unfortunately, increased reforming severity and higher FCC gasoline octane result in a higher aromatics content of the gasoline pool through the production of high-octane aromatics at the expense of low-octane heavy paraffins.
One method of reducing the content of environmentally undesirable aromatic-containing compounds is catalytic aromatic saturation. Several hydrotreating catalysts have been utilized for such operations. A typical catalyst contains hydrogenation metals supported on a porous refractory oxide. This method results in a reduction in octane as well as aromatics. The search continues for better ways to reduce aromatics with less reduction in octane.
U.S. Pat. No. 4,209,383 (Herout et al.) teaches a process combination for benzene reduction using catalytic reforming, catalytic cracking and alkylation of cracked light olefins with aromatics in the reformate.
U.S. Pat. No. 4,647,368 (McGuiness et al.) discloses a method for upgrading naphtha by hydrocracking over zeolite beta, recovering isobutane, C.sub.5 -C.sub.7 isoparaffins and a higher boiling stream and reforming the latter stream.
In U.S. Pat. No. 5,200,059, to UOP, there is disclosed a process combination to reduce the aromatics content and increase the oxygen content of a key component of gasoline blends. The feedstock is contacted with a selective isoparaffin-synthesis catalyst in the presence of hydrogen to form a synthesis effluent with a higher isoparaffin/n-paraffin ratio, separating an isobutane-rich stream, dehydrogenating same and contacting with alcohol to obtain an ether.
U.S. Pat. No. 5,135,639 discloses a process combination to reduce the aromatic content of a key component of gasoline blends. Paraffins contained in catalytic reformates are conserved and upgraded by separation and isomerization, reducing the reforming severity required to achieve a given product. Light reformates may be separated and isomerized and heavier paraffins are separated from the reformate by solvent extraction and adsorption and isomerized.
In U.S. Pat. No. 5,135,902 there is disclosed a catalyst containing nickel, tungsten and phosphorous supported on an amorphous, porous refractory oxide having a narrow pore size distribution for converting hydrocarbon-containing feedstocks.
Another process combination to reduce the aromatics content and increase the oxygen content of a key component of gasoline is disclosed in U.S. Pat. No. 5,198,097. A naphtha feedstock having a boiling range usually suitable as catalytic reforming feed is processed by selective isoparaffin synthesis to yield lower-molecular weight hydrocarbons.
Of the proposed methods heretofore suggested for reducing aromatics a problem has been that a reduction in aromatics is usually accompanied by a decrease in octane.
Some of the more recent references cited above appear to be attempting to address the need in the art for a simple, effective method of reforming gasoline to reduce the amount of benzene and aromatics and increase yields of isoparaffins. None of the available references suggest the possibility of reducing aromatics while, at the same time, maintaining octane, although this would represent a distinct advance in the art.